Interactions of Phytoestrogens with Estrogen Receptors .ALPHA. and .BETA. (III). Estrogenic Activities of Soy Isoflavone Aglycones and Their Metabolites Isolated from Human Urine

Abstract

The intake of weakly estrogenic isoflavonoids (phytoestrogens) is high in countries with a low incidence of estrogenrelated cancers, such as breast and prostate cancers. 1) Two ERs (a and b ) have been identified to date and the physiological responses of estrogens are known to be mediated within specific tissues by at least these two receptors.2,3) The ERs are a 3A member of the nuclear hormone receptor family and act as a ligand-activated nuclear transcription factor. 4)In a previous paper, we reported the results of systematic examination of the estrogenic activities of soy isoflavones (e.g. daidzin, genistin and glycitin) and their metabolites (e.g. daidzein, genistein, glycitein, equol, dihydrogenistein and dihydroglycitein) by enteric bacteria, 5) and the activities of several other isoflavone derivatives isolated from Pueralia lobata and P. thomsonii. 6)Usually, when soy foods are consumed, the soy isoflavones are metabolized into their aglycones and the related compounds by enteric bacteria. We have proved in in vitro experiments that the soy isoflavone glycosides are less estrogenic than the metabolites, i.e., they are activated by enteric bacteria. The metabolites produced by enteric bacteria are absorbed through the intestinal membranes and transported to the liver where they undergo re-metabolization by hepatic enzymes. To evaluate the bioactive compounds in soy products, investigation of the compounds which are actually absorbed within the body is necessary. 7,8) Herein, we describe the results of an investigation on the estrogenic activities of soy isoflavone metabolites isolated from human urine samples. Their effects on the estrogen dependent growth of MCF-7 cells, 9,10) on human ERs (hERs a and b )-dependent b-galactosidase induction, and their binding behavior to hERs were studied. We also examined the estrogenic activities of some synthetic isoflavone sulfates for the purpose of comparison. [2,4,6, H(N)]-17b-Estradiol (72 Ci/mmol) was purchased from Dai-Ichi Pure Chemicals Co. Ltd. RPMI 1640 medium (with or without phenol red), fetal bovine serum (FBS), trypsin/EDTA, Dulbecco's phosphate-bufferd saline (PBS), and kanamycin sulfate were purchased from Lifetech (Rockville, MD, U.S.A.). MATERIALS AND METHODS ChemicalsIsoflavone Metabolites Isoflavone metabolites examined in this work are shown in Fig. 1. M-1-9 were isolated from human urine samples collected for 12 h after feeding soy bean curds.11) Dihydrodaidzein and O-desmethylangolensin (O-DMA) were synthesized following the method described by Wahara et al.12) Genistein 4Ј-O-sulfate (S-1), 4Ј,7-di-Osulfate (S-2), daidzein 4Ј-O-sulfate (S-3), and 4Ј,7-di-O-sulfate (S-4) were synthesized following the method described by Peterson et al. 13)Cells MCF-7 cells were supplied by the Cell Resource Center for the Biomedical Research, Institute of Development, Aging and Cancer, Tohoku University.Growth of MCF-7 Cells MCF-7 cells were cultured in phenol red-free RPMI 1640 medium supplemented with 10% (v/v) FBS and kanamycin sulfate (100 mg/ml) in 25 cm...

Flaxseed attenuates the tumor growth stimulating effect of soy protein in ovariectomized athymic mice with MCF‐7 human breast cancer xenografts

“…In many in vitro studies with MCF-7 cells, soy isoflavones have been shown to increase the proliferation of the cells in concentration dependent manner 6,36,37 and to inhibit apoptosis, 38 which agrees with the findings in MCF-7 xenograft model in vivo showing increased tumor growth via increased cell proliferation after consumption of isoflavone-rich diets. 9,11,22 The mammalian lignan metabolites of plant lignans in FS, enterodiol and especially enterolactone, have also been shown to increase the MCF-7 cell proliferation.…”

“…3,4 The biological effects of lignans have been attributed particularly to enterolactone, which has been suggested to act as an endocrine active compound. In vitro, both soy isoflavones and enterolactone have been demonstrated to interact with estrogen receptor (ER) a and b. Soy isoflavones bind and transactivate both ERs with high affinity 5,6 while enterolactone binds weakly to ERs 7 and activate gene expression via ERs at high concentration. 7,8 Isoflavone and lignan-rich diets are reported to have distinct effects on the growth of estrogen responsive tumors in vivo.…”

A prospective study of vegetarianism and isoflavone intake in relation to breast cancer risk in British women

“…31 However, isoflavones predominantly circulate in conjugated forms 32 and their bioactivity is thought to be markedly less potent than unconjugated forms in terms of binding to the oestrogen receptor and stimulation of transcription. 33 Results from several intervention studies in humans have also suggested that exposure to dietary isoflavones may alter oestrogen metabolism, [34][35][36][37][38][39] although findings from other similar studies have been inconsistent. [40][41][42] Consistent with the null findings in the current study, the majority of previous prospective studies of dietary isoflavone intake and risk for breast cancer have failed to find a strong association, [10][11][12]43 while results from one study suggested a protective association.…”

Phytoestrogens in bovine plasma and milk - LC-MS/MS analysis

“…The putative beneficial health effects of isoflavones are based on their structural similarity to the mammalian estrogen 17β-estradiol. Due to this analogy, they may compete with estrogens in binding to estrogen receptors and show weak estrogenic activities (Kinjo et al 2004).…”